TradingCalcPrediction Market Arbitrage Checker
CROSS-VENUE ARBITRAGE · KALSHI, POLYMARKET, ADI PREDICTSTREET, LIMITLESS, MYRIAD · FEE-AWARE
Check whether the same real-world bet's price gap across venues is a guaranteed, direction-independent profit, which side to buy where, and whether a realistic trading fee erases it.
Each quote must genuinely be the same real-world bet on a different venue. Assumes each venue's own No price is 1 minus its own Yes price - the standard complementary-binary convention, not necessarily an exact live No-side quote.
What is cross-venue arbitrage?
When two venues quote different prices for the same real-world bet, buying "Yes" at whichever venue quotes it cheapest and "No" at whichever venue quotes "Yes" most expensively (so its own "No" is cheapest) locks in a $1 payout regardless of the outcome. If the total cost of both legs is under $1, the difference is a guaranteed, direction-independent profit.
The formula
- costPerPair = cheapestYesPrice + (1 − priciestYesPrice), each × (1 + feePctPerLeg)
- guaranteedProfit = stake × (1 / costPerPair − 1), only when costPerPair < 1
Assumes each venue's own "No" price is 1 minus its own "Yes" price, the standard complementary-binary convention. A nonzero spread between two venues is, in this idealized no-fee model, exactly an arbitrage of that size, this is the same math the Spread Checker already reports, made actionable (which side to buy where) and fee-aware.
Worked example
Venue A quotes Yes at 60%, Venue B quotes Yes at 55%, $1,000 stake, no fees:
- Buy Yes at B: $0.55/share. Buy No at A: $0.40/share (1 − 0.60)
- costPerPair = 0.95, guaranteed profit = $1,000 × (1/0.95 − 1) = $52.63
A real trading fee can erase this: at a 6% per-leg fee, costPerPair rises to 1.007, and the arbitrage disappears entirely, this calculator reports that honestly instead of always showing a positive number.
Where to go next
Just want to see the raw spread without the arbitrage math? Spread Checker. Betting your own probability estimate against one venue instead of two venues against each other? Kelly Calculator.
Use via API or MCP
This calculation is available as a deterministic API call: useful for bots or AI agents that need to check for cross-venue arbitrage before committing capital.
How is this different from the Spread Checker?
The Spread Checker reports the raw percentage-point gap between venues. This tool turns that gap into an action: which side to buy at which venue, how many shares, the exact guaranteed dollar profit for your stake, and whether a realistic trading fee would erase it.
Is a nonzero spread always a real arbitrage?
In the idealized model this calculator uses (each venue's own No price is exactly 1 minus its own Yes price, no fees), yes, mathematically. In practice, trading fees, a genuinely separate No orderbook at one venue, or execution slippage can erase a real-looking spread, which is exactly why feePctPerLeg exists here.
What does costPerPair mean?
The total cost to buy one "Yes" share at the cheapest venue and one "No" share at the venue where No is cheapest (i.e. the priciest Yes venue), together guaranteeing exactly $1 back regardless of which outcome happens. Arbitrage exists only when this is under $1.
Can I use manual probabilities instead of live venue lookups?
Yes. Manual mode takes 2-5 probabilities you already know, with no live fetch, useful when you've already checked prices elsewhere or want to test a hypothetical.